The present invention relates to a digital photography system and method of using the system to provide electronic still photographs. The invention more particularly relates to a shutterless single lens digital still camera and method of automatically adjusting the exposure of the camera in high and low ambient lighting conditions.
With the advent of small low cost digital storage devices, digital still cameras are rapidly replacing silver halide film cameras as the camera of choice. In this regard, such low cost digital storage devices are enabling digital cameras to provide high resolution electronic still photographs. Moreover, with the current improvements in ink jet and laser printer technologies, inks, paper, and image reproduction processes are allowing color prints to be generated from captured digital images that are of substantially the same quality as that provided through silver halide color prints.
While digital still cameras have been replacing silver halide color print cameras as the preferred choice of the consumer, one of the biggest drawbacks with most, if not all digital cameras, has been size. That is, in order for a user to capture and review an electronic still image such digital devices have incorporated large, bulky and expensive liquid crystal display units and other light converting devices, such as charge coupled devices and the like. More particularly, in order for a user to preview an image to captured, the digital camera must give feedback to a user of what area of a scene to be photographed will be captured when a picture is taken. This has traditionally been accomplished using a built-in device called an optical viewfinder or optical window that enables the user to visualize the scene and see exactly what area of the scene that will be captured by the camera lens system. The ability of providing an accurate representation of the image to be capture has been implemented in two different manners between what is known in the state of the art as a through the lens (TTL) camera and a point and shoot (PAS) camera.
In the TTL camera, as a user views a scene to be photographed, he or she utilizes the camera viewfinder. More particularly, the user is viewing the scene through the lens system of the camera. That is, with the help of an internally positioned mirror within the TTL camera, the light passing through the lens system is reflected by the internal mirror and directed to the optical viewfinder for consideration by the user. When the user is satisfied with the scene to be captured, the mirror is repositioned allowing a direct light path to the photosensitive plane of the camera, and thus, allowing the scene to be captured as viewed through the optical viewfinder.
The PAS camera is much less expensive and does not allow the user to view the scene through the primary lens system. Instead, the optical viewfinder is provided with a secondary lens system that moves in and out in tandem with the primary lens system. In short then, in the PAS camera two separate light paths are established; one light path for the primary lens system to the photosensitive plane of the camera and another light path through the secondary lens system to the viewfinder for the scene preview benefit of the user.
In either implementation whether TTL or PAS, once the user has captured the image, the user can then only view the captured image by switching the camera mode of operation from a preview mode of operation to a review mode of operation. The change in the mode of operation permits the user to view the previously stored captured images on a liquid crystal display panel of the camera.
Therefore it would be highly desirable to have a new and improved digital camera that would permit the user to immediately view a captured image without switching the mode of camera operation and without the need of viewing the image on an externally mounted liquid crystal display device.
In accordance with the present invention, a shutterless single lens digital still camera includes an internal processor and auto exposure algorithm that automatically adjusts the exposure of the camera in high and low ambient lighting conditions. The auto exposure algorithm causes the camera to generate a signature of a current ambient luminance level and then in response to the signature to generate automatically an exposure setting.